Conjugated polymer semiconductors may find application in optoelectronic and electrochemical devices, such as photovoltaic cells, light emitting diodes, sensors, electrochromics, and field-effect transistors. Polymeric materials can offer numerous advantages including access to a flexible and/or light-weight device and/or the ability to fabricated the device in large area formats using low-cost processing techniques (e.g., solution processing). For electrochemical devices, the electron-donating or electron-accepting properties of the conjugated polymers are important. Although many varieties of high performance p-type (electron donor) polymers are available, suitable n-type (electron acceptor) polymers remain largely elusive.
Relatively few studies have been reported concerning heterojunctions between p/n-type polymers for photovoltaic cells, mainly due to the limited n-type polymers with appropriate levels of electron affinity (EA). As a result, organic polymer photovoltaic devices generally employ fullerene acceptor molecules as the n-type material. Use of fullerene derivatives is disadvantageous because of the relatively weak absorption in the visible and near-infrared regions.
Accordingly, improved methods and compositions are needed, including novel n-type polymeric materials